It is known in high pressure hydraulic systems to provide a hydraulic damping assembly damping pressure oscillations. The damping assembly is equipped with flow restrictors in two flow paths. The flow restrictors may be two flow restrictors having fixed cross-sections, or one flow restrictor having a fixed cross-section and a flow restrictor having a variable cross-section, or even two flow restrictors having variable cross-sections. Such damping assemblies e.g. are known for load holding valves of hydraulic consumers or are applied in regulating systems of variable displacement pumps. In the latter case the hydraulic damping assembly influences the dynamic performance of the variable displacement pump, e.g. in order to minimise or eliminate overshooting.
In a regulating system of a variable displacement pump as known in practice a flow restrictor having a variable cross-section is arranged in a discharge flow path extending from an actuating piston of the variable displacement pump to the low pressure side and a further flow restrictor having a variable cross-section is arranged in a discharge path extending from a 3/2-multi-way slider valve to the low pressure side, respectively. The 3/2-multi-way slider valve regulates, e.g. in dependence from load pressure, the actuation of the pump actuating piston via the supply pressure and a pressure relief of the actuating piston to the lower pressure side. The damping effect is executed with the help of internal leakage flows across the flow restrictors having variable cross-sections. Each of the flow restrictors having a variable cross-section contains an adjustment element in order to allow to set the cross-section of the restrictor upon demand. An optimum absorption of pressure oscillations within the regulating system of the variable displacement pump e.g. needs to consider the imminent requirements of the system in the connection with internal leakage at the discharge side of the actuating piston and internal leakage at the discharge side of the 3/2-multi-way slider valve, i.e., to increase the respective other cross-section of one flow restrictor when the cross-section of the one flow restrictor decreases. In the case that tunings are to be carried out at both adjustment elements of both flow restrictors, it is complicated to carry out relatively accurate adjustments according to imminent system specifications in the regulating system. Such adjustments need a great deal of knowledge of the system and expertise and are time consuming as then an effect of an adjustment carried out can only be determined during operation of the regulating system. Any adjustments then merely lead to a compromise of the ratio between the final cross-sections of both flow restrictors. This is a consequence of the fact that the producer of the regulating system is aware of the imminent specifications of the system, but has no influence on adjustments carried out later by the user of the regulating system. In addition, two flow restrictors having variable cross-sections and their own adjustment elements require larger structures.
EP 0 084 835 A discloses a regulating system of a variable displacement pump. A 4/3 feedback multi-way valve is provided in order to carry out pilot pressure control of a multi-way valve provided for two actuating cylinders of the variable displacement pump. The feedback multi-way valve is actuated in dependence from the pressure supplied to one of the actuating cylinders. A neutral position can be adjusted in the feedback multi-way valve in which neutral position both pilot pressure sides of the multi-way valve are commonly pressure relieved to the tank via two flow restrictors having fixed cross-sections. When the feedback multi-way valve switches out of the neutral position the flow restrictors having fixed cross-sections become blocked by the valve element of the feedback multi-way valve.
In a control device known from JP 50-132501 A the control device is supplied with pressure medium by a variable displacement pump. A pressure compensator is provided parallel to a multi-way valve. The pressure compensator is either actuated manually by a hand lever or is actuated by pilot pressures. The multi-way valve controls the pressure actuation of a hydro-consumer by the variable displacement pump. In the pressure compensator a piston is co-operating with two lands alternatively orifice-like with exit ports in order to connect a pressure port either with the tank or with a continuing pilot channel.
EP 1 577 563 A discloses a hydraulic control device for a working machine which hydraulic control device is supplied by a variable displacement pump. A main circulation valve is arranged between the variable displacement pump and the tank. The main circulation valve is actuable via a solenoid valve in order to relieve hydraulic medium either directly to the tank or to direct the hydraulic medium to a group of multi-way valves for different consumers. Each multi-way valve of the group contains a through flow channel to the tank which, in the neutral position of the multi-way valve, is directly open to the tank and which then is blocked rapidly when the multi-way valve switches out of the neutral position.
GB 1 095 347 A relates to a fluid pressure servomechanism including a valve in which a rotatable valve element when rotated simultaneously adjusts two flow restrictors having variable cross-sections in opposite directions.
DE 32 37 452 A discloses a control and regulating assembly for a settable hydrostatic unit. The unit contains a hydrostatic motor as a drive source of a pressure line in order to produce nearly constant pressure. The hydrostatic motor drives via an output shaft an auxiliary control pump serving as a speed signal emitter. A pilot pressure line of the fixed displacement auxiliary control pump is connected to the tank via a flow restrictor having a variable cross-section. An exit line of the hydromotor which drives the auxiliary control pump is connected to the tank via a multi-way regulating valve and a further flow restrictor having a variable cross-section in order to actuate a setting cylinder of the hydromotor. Both flow restrictors having a variable cross-section may be interconnected so that they can be adjusted inversely to each other. However, the flow restrictors having variable cross-section do not absorb pressure oscillations but are used for setting the target speed of the hydromotor in both directions of rotation.